This application is based on and claims priority under 35 U.S.C. xc2xa7119 with respect to Japanese Application No. 11(1999)-82101 filed on Mar. 25, 1999 and Japanese Application No. 11(1999)-113904 filed on Apr. 21, 1999, the entire content of both of which is incorporated herein by reference.
The present invention generally relates to vehicle braking systems. More particularly, the present invention pertains to a vehicular braking force control apparatus which adjusts the fluid pressure of a wheel brake while a braking operation is performed and which supplies fluid pressure to the wheel brake and adjusts it while no braking manipulation is performed.
One example of a vehicular braking force control apparatus is disclosed in German Unexamined Patent Publication No. 4,336,464. This vehicular braking force control apparatus has a fluid pressure generation device for generating a fluid pressure corresponding to the braking manipulation or operation force, a brake pipe that is connected to at least one wheel brake, and a high-pressure pump for drawing operation fluid from a reservoir and transporting it to the wheel brake at least indirectly. The reservoir is coupled with the brake pipe at least indirectly on the liquid pressure generation device side. The high-pressure pump is connected to the reservoir at least indirectly on the suction side. The apparatus also includes a bendable partition element or diaphragm provided in the reservoir. The diaphragm is bendable in the sucking direction of the high-pressure pump and is bent or deformed by a pressure that is supplied from the brake pipe. This apparatus has an advantage that it can reduce suction ripples of the pump with a relatively simple structure.
However, with the reservoir provided with the bendable partition element or diaphragm, the amount of bending of the diaphragm is limited. To obtain a volume variation that is necessary and sufficient for absorption of ripples, the size of the diaphragm should be increased. To avoid increasing the size of the diaphragm, the thickness of the diaphragm needs to be reduced, in which case sufficient ripple absorption performance may not be attained. Further, the amount of bending associated with the diaphragm tends to vary widely, which leads to the concern that considerable dispersion occurs in the ripple absorption effect.
A need thus exists to be able to reliably reduce suction ripples without increasing the apparatus size.
According to one aspect of the present invention, a vehicular braking force control apparatus includes a liquid pressure generating device for generating a liquid pressure in accordance with a brake manipulation force, a main reservoir for supplying operation liquid to the liquid pressure generation device, a wheel brake receiving the output liquid pressure of the liquid pressure generation device for braking a wheel, a main passage connecting the liquid pressure generation device to the wheel brake, a liquid pressure adjustment device connected to the wheel brake for adjusting the liquid pressure of the wheel brake, and an electrically-driven pump having a suction side that is connected to the liquid pressure adjustment device. A suction passage connects the suction side of the electrically-driven pump to the liquid pressure adjustment device, and a discharge passage connects the discharge side of the electrically-driven pump to the main passage at a point between the liquid pressure generation device and the liquid pressure adjustment device. A first solenoid valve, which operates in synchronism with discharge of the electrically-driven pump, is provided in the main passage between the liquid pressure generation device and a connecting point where the discharge passage is connected to the main passage. An auxiliary suction passage connects the liquid pressure generation device to the suction side of the electrically-driven pump. A second solenoid valve, which operates in synchronism with discharge of the electrically-driven pump, is provided in the auxiliary suction passage between the liquid pressure generation device and the suction side of the electrically-driven pump. A first check valve is provided in the auxiliary suction passage between the second solenoid valve and the suction side of the electrically-driven pump for allowing passage of operation liquid only from the side of the second solenoid valve to the suction side of the electrically-driven pump. An auxiliary reservoir is located in the suction passage between the liquid pressure adjustment device and the suction side of the electrically-driven pump for storing operation liquid. A low-pressure reservoir provided in the auxiliary suction passage between the second solenoid valve and the first check valve reduces the suction ripple by reducing the pressure at the suction side of the electrically-driven pump in the auxiliary suction passage. The low-pressure reservoir includes an operation liquid portion that communicates with the auxiliary suction passage and an air portion where air exists, with the low-pressure reservoir being partitioned into the operation liquid portion and the air portion by a partition member. The air portion is provided with a spring member for pressing the partition member toward the side of the operation liquid portion.
In a state that the first solenoid valve is closed and the second solenoid valve is opened, while operation liquid is pressurized by the electrically-driven pump, a check valve closest to the suction side of the electrically-driven pump is opened and closed intermittently because the electrically-driven pump sucks operation liquid intermittently. In this operation, the movement of operation liquid being sucked by the electrically-driven pump is abruptly stopped by the check valve. The liquid pressure generation device continues to output operation liquid, and the operation liquid tends to flow into the auxiliary suction passage by a volume larger than the discharge capacity of the electrically-driven pump. As a result, the liquid pressure of the auxiliary suction passage quickly increases and a surge pressure normally occurs. That is, the intermittent opening and closing of the check valve successively normally causes surge pressures in the auxiliary suction passage. This is a phenomenon called suction ripples, whose amplitude is several times greater than the liquid pressure in the auxiliary suction passage.
With the present invention, however, the ripple absorption low-pressure reservoir is provided and has an operation liquid accommodation capacity that varies through expansion/contraction of the spring member. Therefore, even if operation liquid flows into the auxiliary suction passage by a volume larger than the discharge capacity of the electrically-driven pump, part of the operation liquid is temporarily accommodated in the operation liquid portion of the ripple absorption low-pressure reservoir and hence the liquid pressure of the auxiliary suction passage does not unduly increase. Therefore, the liquid pressure in the auxiliary suction passage is kept low and hence the absolute value of the suction ripples is reduced to a small value. Another advantage obtained is that ripple energy is absorbed by the sliding of the partition member and contraction of the spring member of the low-pressure reservoir. Further, because the spring member is small in the dispersion of the bend amount and can store large elastic energy in spite of its small size, the dispersion of its ripple absorption ability is small and the apparatus can be miniaturized.
In a preferred form of the invention, the second solenoid valve is a solenoid valve incorporating an orifice. With this construction, the liquid pressure generated by the liquid pressure generation device is reduced by the second solenoid valve and hence the liquid pressure in the auxiliary suction passage is kept low. This, together with the advantages mentioned above, reduces the absolute value of suction ripples to a small value.
The second solenoid valve can be a linear solenoid valve in which the degree of opening varies continuously. The volume of operation liquid flowing from the liquid pressure generation device into the auxiliary suction passage can thus be relatively precisely controlled to be smaller than the maximum accommodation capacity of the ripple absorption low-pressure reservoir, and the liquid pressure of the auxiliary suction passage does not increase excessively. Therefore, the liquid pressure in the auxiliary suction passage is kept low and hence the absolute value of suction ripples is reduced to a small value.
The second solenoid valve can also be a flow adjustment valve that adjusts the volume of operation liquid flowing into the electrically-driven pump in accordance with the liquid pressure generated by the liquid pressure generation device. The volume of operation liquid flowing from the liquid pressure generation device into the auxiliary suction passage can thus be relatively precisely be controlled and the liquid pressure of the auxiliary suction passage does not increase excessively. Therefore, the liquid pressure of the auxiliary suction passage is kept low and so the absolute value of suction ripples is reduced to a small value.
The vehicular braking force control apparatus can also include a second check valve between the second solenoid valve and the low-pressure reservoir for allowing passage of operation liquid only from the second solenoid valve side toward the low-pressure reservoir side. This makes it more difficult for suction ripples in the auxiliary suction passage to be transmitted to the liquid pressure generation device side.
According to another aspect of the present invention, a vehicular braking force control apparatus includes a liquid pressure generation device for generating a liquid pressure in accordance with the brake manipulation force, a main reservoir for supplying operation liquid to the liquid pressure generation device, a wheel brake receiving the output liquid pressure of the liquid pressure generation device for braking a wheel, a main passage for connecting the liquid pressure generation device to the wheel brake, a liquid pressure adjustment device connected to the wheel brake for adjusting a liquid pressure of the wheel brake, an electrically-driven pump having a suction side connected to the liquid pressure adjustment device, a suction passage connecting the suction side of the electrically-driven pump to the liquid pressure adjustment device, and a discharge passage connecting a discharge side of the electrically-driven pump to the main passage at a point between the liquid pressure generation device and the liquid pressure adjustment device. A first solenoid valve, which is operational in synchronism with discharge of the electrically-driven pump, is provided in the main passage between the liquid pressure generation device and a connecting point where the discharge passage is connected to the main passage. An auxiliary suction passage connects the liquid pressure generation device to the suction side of the electrically-driven pump, and a second solenoid valve is provided in the auxiliary suction passage between the liquid pressure generation device and the suction side of the electrically-driven pump. The second solenoid operates in synchronism with discharge of the electrically-driven pump and is a linear solenoid valve in which the degree of opening varies continuously. An auxiliary reservoir is provided in the suction passage between the liquid pressure adjustment device and the suction side of the electrically-driven pump for storing operation liquid. This configuration makes it possible to precisely control, with a simpler structure, the volume of operation liquid flowing from the liquid pressure generation device into the auxiliary suction passage so that it becomes smaller than the maximum accommodation capacity of the low-pressure reservoir. Therefore, the liquid pressure of the auxiliary suction passage is kept low and hence the absolute value of suction ripples is reduced to a small value.
The braking force control apparatus can also be provided with an actuator acting on the liquid pressure generation device for causing the liquid pressure generation device to generate a liquid pressure also when receiving no brake manipulation force. By pressurizing (pre-charging) the auxiliary suction passage, the suction performance of the electrically-driven pump is improved and hence the response speed of the pressurization control by the electrically-driven pump is increased.
According to another aspect of the invention, a vehicular braking force control apparatus includes a liquid pressure generation device for generating a liquid pressure according to a brake manipulation force, a main reservoir supplying operation liquid to the liquid pressure generation device, a wheel brake receiving the liquid pressure output from the liquid pressure generation device for braking a wheel, a main passage connecting the liquid pressure generation device to the wheel brake, a solenoid valve disposed in the main passage for adjusting liquid pressure in the wheel brake, an electrically-driven pump having a suction side connected to the liquid pressure adjustment device, a suction passage connecting the suction side of the electrically-driven pump to the liquid pressure adjustment device, a discharge passage connecting the discharge side of the electrically-driven pump to the main passage, and an auxiliary suction passage connecting the liquid pressure generation device to the suction side of the electrically-driven pump. A solenoid valve, operational in synchronism with discharge of the electrically-driven pump, is provided in the auxiliary suction passage between the liquid pressure generation device and the suction side of the electrically-driven pump. A low-pressure reservoir is provided in the auxiliary suction passage between the solenoid valve that is disposed in the auxiliary suction passage and the suction side of the electrically-driven pump for reducing suction ripple by reducing a pressure at the suction side of the electrically-driven pump in the auxiliary suction passage. The low-pressure reservoir includes an operation liquid portion that communicates with the auxiliary suction passage and an air portion in which exists air. The low-pressure reservoir is partitioned into the operation liquid portion and the air portion by a partition member, and a spring member is provided for pressing the partition member toward the operation liquid portion.